Computing devices provide us ever greater features and types of applications. While early applications were very numbers-based and centered around paper cards or punch tapes, eventually they added video display monitors and text input (via keyboard) and output became a central tenet of computer operation. Eventually, graphical user interfaces were developed that added color and other visual richness to computer applications, and even allowed the development of applications that could visually replicate certain real world systems.
Computer applications also continue to advance in complexity, and in the types user interfaces that are generated to improve the experience that a user has in interacting with the applications. For example, electronic book reader applications can display text at different sizes that correspond to a reader's particular needs. In addition, some applications provide a page turning experience that looks like an actual paper page being bent and turned, and then laid flat again.